Stationary airfoils disposed aft of a rotor section within a gas turbine engine help direct the gas displaced by the rotor section in a direction chosen to optimize the work done by the rotor section. These airfoils, commonly referred to as “guide vanes”, are radially disposed between an inner casing and an outer casing, spaced around the circumference of the rotor section. Typically, guide vanes are fabricated from conventional aluminum as solid airfoils. The solid cross-section provides the guide vane with the stiffness required to accommodate the loading caused by the impinging gas and the ability to withstand an impact from a foreign object.
“Gas path loading” is a term of art used to describe the forces applied to the airfoils by the gas flow impinging on the guide vanes. The magnitudes and the frequencies of the loading forces vary depending upon the application and the thrust produced by the engine. If the frequencies of the forces coincide with one or more natural frequencies of the guide vane (i.e., a frequency of a bending mode of deformation and/or a frequency of a torsional mode of deformation), the forces could excite the guide vane into an undesirable vibratory response. The guide vanes are secured between the inner and outer cases of a turbine engine case by a series of bolts.
Historically, the undesirable vibratory response at times excites the guide vane so much that the guide vane pulls the bolts through the outer case and cracks the case. As a result, the aircraft must be taken out of service in order to repair and/or replace the case and other necessary components.
Therefore, there exists a need to secure the guide vane to the outer case in order to prevent cracking or mitigate existing cracking or cracks.